Adenomyoepithelial adenosis and low-grade malignant adenomyoepithelioma of the breast

Adenomyoepithelial adenosis of the breast is a form of adenosis not previously described. It is similar in several ways to microglandular adenosis, but one significant difference is the presence of myoepithelial cells. The present case originated as adenomyoepithelial adenosis in a 46-year-old woman. In the course of 18 years it proliferated and changed into a low-grade malignant adenomyoepithelioma. Electron microscopy confirmed the presence of myoepithelial cells in the adenosis, and immuno-histochemical study demonstrated cells containing actin (representing myoepithelial cells) in the adenosis as well as in the adenomyoepithelioma.